For securing tubes, cables and the like, Protex says that its Bandclamp is perhaps the only available method of rapidly clamping small diameters

Why does the Bandclamp score over the old-established and arduous worm-drive hose clip?

The answer, it seems, is because it can be opened and closed repeatedly over long service intervals, it may be released completely and it is fast to operate. For rapidly clamping small diameters in the range 110 to 25mm, it is arguably the only solution available. The simple platform type with spring claw, made in stainless or zinc-plated mild steel, offers custom band diameters from 110 down to 40mm. The maximum spring load is 65kg at a 1.5mm extension.

Technically described as an overcentre, lever-action fastener, there are many variants: Protex is one of only about 10 manufacturers worldwide and supplies around 500 individual catalogue items, plus variations, specials and alternative finishes. Variations include with or without a platform or saddle and mounted on a flexible, custom-made, stainless steel band. Some have an optional safety catch to prevent accidental opening. They can be released fully or made captive.

The variations in design are not to accommodate different diameters of substrate, but because of the pressure to be borne. For example, the 60-1750/PBC And 61-1750/PBC models are down to 25mm diameter. They are pressure tested up to the highest pressure that bandclamps can sustain – 6.5bar (100psi). To accommodate such an elevated pressure, these models have both a special strengthening saddle (a semi-circular shoe) and a triangular platform with a reinforcing ribbed plate underneath.

To make certain applications easier to accommodate, some models of the platform type are also designed with a captive catchplate and hinge built into the band.

Many bandclamps also actually incorporate a worm-drive hose clip – a device with which they normally compete – for extended adjustment (10 times the normal value). Others are in kit form for self-assembly, because users cannot always predict the required diameter in advance.

Uses exist in automotive engineering, chemical, pharmaceutical, food and water and waste treatment industries. Bandclamps are used to secure rubber hoses and tubes and other items, and to facilitate regular Health & Safety examination of exhaust ventilation plant.

•  Protex

October 1999

How much torque should be put into a joint? This value is often not defined, so a design engineer often has to base the value on experience and values which the fastener manufacturer may recommend. It is also possible to establish the approximate optimum torque by a trial and error method:

• 1 Take a small number (say, 10-20) of new screws and make sure they are free of any lubricant. Using the screwdriver, tighten the fasteners to within 10% of the estimated torque.
• 2 The assemblies should then be subject to normal service loadings, including vibrations, temperature changes, etc. Note any loosening or relaxation in the joint. Adjust the screwdriver torque level and repeat the test with new screws and components until total joint integrity in service is achieved.
• 3 The establish the ultimate over-torque level by applying a low friction lubricant to the screw threads and hand tightening them to specified torque +10%. Observe the degrees of rotation in the screw in case they suddenly increase, indicating “necking” or fatigue in the screw. Then continue to apply torque until either the thread strips or the screw head breaks off.
• 4 The established safe torque should then be inserted on the production drawings.

Fastener torque values

Clamping force is what actually keeps a joint together and applying torque to a threaded fastener achieves this clamping force by using the thread pitch to pull the screw head down onto the surface of the work place. The table shows recommended torque values for metric fasteners of different tensile strengths or grades. The values shown are for lightly oiled, plain steel screws, having a coefficient of 0.125. The most common grade is 8.8, but 10.9 and 12.9 are also used. It is not recommended that grades below 8.8 are used for machine screws which will be assembled by power tools.

Screwdrivers and Screwdriving is a handy, 24 page, A5 guide to component jointing using threaded fasteners from Desoutter. Its five main sections cover: Threaded Fasteners (illustrating the different types of self-tapping screws and screwheads); Types of Joint; Torque, Screwdriving Tools; and Problem Solving. Single copies are available free of charge by circling the enquiry number immediately below. Also, to assist manufacturers in building up training programmes, the company tells us that the material is available in 8.5 x 11in format for copying onto overhead transparencies.

• Desoutter
• Tel: 0181 205 7050
• Fax: 0181 205 5167

An innovative approach to sealing or potting electromechanical components comes from US company Multi-Seals – solid pre-forms that melt when heated to form a seal

Precision epoxy preforms are one-part resins that offer a no mix no mess solution to the problem of sealing and potting small parts such as electromechanical components. Solid at room temperature when heated they melt and cure forming a consistent seal that protects components from dust moisture oil solder flux and conformal coatings. They can withstand high soldering temperatures and all of the most common industrial cleaning solvents.

The heat is applied for a specified time depending on the shape size and material used first to melt then to flow and finally to cure the material which is always an electrical grade epoxy or epoxy-phenolic. This method eliminates mixing and metering of two-part liquid epoxies as well as the viscosity variations that can occur. Available shaped include rings rectangles ovals ellipses and triangles. Custom preforms can also be designed and manufactured to suit specific application requirements.

Best curing results are obtained using a forced convection oven preheated to the appropriate cure temperature. A mechanical convection (air circulating) oven allows for the fastest recovery and the most consistent means of heat transfer. The oven should be calibrated at least once a year.

Typically 150 is a good starting point. Adequate cure for most applications will take between 30 minutes and two hours depending upon the grade. Allowances should be made for oven recovery time and component mass including loading trays.

For production purposes adequate cure schedules should be determined experimentally and then strictly adhered to. This is done by placing thermocouples throughout the oven to determine the effects of component mass. The longest time it takes for any of the thermocouples to reach cure temperature should be added to the listed cure times in the data sheets. Adding an additional 5-10 minutes is also recommended.

Preforms need to be stored in a cool dry area and in closed containers when not in use. An air-conditioned office is best but not absolutely necessary. Refrigeration can cause condensation of improperly handled.

The preforms can be dispensed at rates of 200 to 600 using automatic or semi-automatic equipment though they can of course be applied manually as well. Templates pick and place machines and bowl-fed gravity tracks are all viable loading methods for dispensing epoxy preforms.

• Multi-Seals
• Kenneth Harvill
• 00 1 860 643 7188

September 1998

In a tensioner designed as a replacement for a hex nut, Alan Quinn uncovers a new solution to an old problem

It’s an old problem: torquing large bolts to capacity with hand tools. The strength of a screw fastener increases with the square of its diameter. To make use of the strength, it is necessary to torque the fastener until it is pre-stressed to a pre-determined level. But while the strength of the fastener increases in the second power of the diameter, the torque required for pre-stressing increases in the third power. Hence, the torque exerted by ordinary torquing devices, such as hand wrenches, torque wrenches and air impact wrenches is limited. For example, bolts greater than 25mm diameter cannot be effectively torqued to capacity with hand tools.

The solution? Superbolt tensioners from Furmanite Silk Engineering are designed as direct replacements for hex nuts. They can be threaded onto a new or existing bolt, stud, threaded rod or shaft.

The main thread serves to position the tensioner on the bolt or stud against the hardened washer and load-bearing surface. Once positioned, the actual tensioning is accomplished with simple hand tools – standard torque wrenches or air tools can generate higher bolt tensions than any other bolting method available – by torquing the jackbolts that encircle the main thread.

Time savings

These simple mechanical devices cost comparatively less than other bolting methods. The number of jackbolts has proven not to be a concern. Some quite significant time savings during installation or removal can be realised, according to the company. Total man hours and downtime can be reduced. Multiple workers can be used for even faster installation or removal.

Properly torqued, Superbolt products will not loosen. Pre-stressed tensioners on bolts or studs should remain tight on vibrating, pulsating or reciprocating equipment, eliminating downtime due to bolting.

Superbolt tensioners eliminate many common injuries which can be associated with other bolting methods.They have been used in awkward locations such as overhead bolts, on top of large equipment and also in hazardous environments such as nuclear power plants.

Most applications can utilise standard Superbolt products. However, specials can be designed to fit a wide variety of limited space applications.

Superbolt tensioners add elasticity to any bolted joint. The joint becomes more resistant to thermal or dynamic cycles. They provide precise tightening control, which is critical for sensitive applications, such as gasketed flanges.

Thread galling and stud seizure are eliminated, due to tightening in pure tension. This prevents the difficulties later to be encountered with removing frozen studs.

• Furmanite Silk Engineering 

October 1999

By measuring the clamping force of threaded fasteners, says ROY MOFFATT, you can be more confident of bolts or studs performing to expectations than you can by relying on a torque wrench alone

How many products rely on threaded studs or bolts for their proper operation? Consider, for instance the importance of correctly tightening the bolts in a joint which incorporates a gasket. Too little clamping force and the gasket might as well not be there. Too much force, on the other hand, and we have stripped the thread.

The conventional way to try to guarantee that the bolts or studs are doing their job properly would be to tighten them to a specified value using a torque wrench. But the problem with this method is that it will not necessecarily produce the correct clamping force. This method is inaccurate because the torque figure will depend far more on the design of the fastener and the prevailing frictional conditions than it will on the clamping action. Only a small proportion of the applied torque is actually used to extend the bolt, so even under ideal conditions with a perfectly calibrated torque wrench errors of the order of 50% can and do occur.

According to recently published figures, loose fasteners cause 23% of all service problems in the automobile industry, and as many as 12% of new cars have problems with incorrectly tightened fasteners.

The ideal way to measure the clamping force in a fastener is to measure it directly by means of strain gauges. Variohm is now able to offer this service on bolts down to 5mm diameter.

In order to provide the best accuracy as well as the best environmental protection, the gauges are placed in holes drilled down the longitudinal axis of the bolt or stud. These holes can be as small as 4mm diameter.

Fastening performance

Drilling bolts in this manner doesn’t normally affect their fastening performance since the hold only protrudes into the plain part of the body which, even with the hole in it, is still far stronger than the thread. It is the thread, therefore, which is limiting the force the bolt can apply. On a stud, which is normally threaded both ends, some de-rating does occur, but this can normally be offset through the selection of a different material.

Gauges installed by this method sit on the bolt’s neutral axis where errors due to torsion or bending are at a minimum whereas the tensile force is at a maximum, so accuracy is enhanced linearity in the order of a fraction of a percent is quite normal.

Being placed at the centre of the bolt or stud, the gauges are not as subject to radiant heat as they would be if mounted on the surface. Conduction means that the heating effect will be slower and more even, so that the strain gauge bridge doesn’t suddenly go out of balance whenever the temperature changes.

If the figures quoted for the automotive industry are correct, then this technology could offer far reaching benefits. Consider, too, what it could offer to aerospace research and testing. Areas such as nuclear engineering would be another typical application for this type of technology.

• Variohm Components

April 2000

What’s the best compression limiter for your application, and what points should you bear in mind? Here are a few simple guidelines

Compression limiters protect the plastic components of an assembly from compressive loads generated by bolt tightening. The objective is to keep compressive stresses below the elastic limit of the plastic, preventing unwanted distortion and cracking. In practice, as the bolt is tightened, the plastic compresses and the stress in the plastic increases until the head of the bolt (or washer if one is used) comes into contact with the compression limiter. Thereafter, the compression limiter and plastic will compress at the same rate. The compression limiter will absorb additional clamping loads without further significant compression and increased stress in the plastic material.

There are two basic types of standard compression limiter: split seam and solid knurled. The split seam type is produced from carbon steel in heat-treated and non-heat-treated versions. In the Spirol Industries range, these are designated Series CL250 and Series CL200 respectively. The solid knurled type is produced from brass in symmetrical and headed versions, Series CL100 and CL110 respectively. Since these compression limiters are designed to meet specified proof loads, the dimensional specifications are different. The split seam design has a lead to aid insertion. The solid design has a pilot, allowing it to stand freely in the hole prior to complete installation.

A properly designed bolted joint must meet the following criteria:

• The head of the bolt (or washer) should always seat against the compression limiter under load. This will prevent deterioration of the bolted joint resulting from diminishing clamping load due to plastic creep

• The compression in the plastic component should not exceed its elastic limit, when compressed to seat the bolt against the compression limiter in the worst-case tolerance condition of the assembly

• To ensure that the compression limiter will not yield prior to the bolt under excessive clamping loads, the proof load of the compression limiter should be equal to or greater than the proof load of the bolt

• The clearance between the maximum bolt diameter and the minimum installed inside diameter of the compression limiter should be sufficient to compensate for normal misalignment.

The Inserts and Tubular Products Divisions of Spirol Industries have joined forces to produce a 12-page design guide to assist design engineers in the selection of compression limiters for their plastics components applications.

The recommended maximum length of the compression limiter is the minimum thickness of the plastic component. The compression of the limiter at the recommended tightening torque assures that there will always be some compression on the plastic component.

The recommended minimum length of the compression limiter is the maximum thickness of the plastic component, minus the maximum allowable compression of the plastic component, plus the compression of the compression limiter at the proof load.

A further determination needs to be made to verify that, at the recommended clamping load, the head of the bolt (or washer if one is used) will seat itself against the compression limiter at the maximum tolerance condition.

• Spirol

July 2000

A new all-plastic integral spring design enables objects such as cables, tubing, paper and labels to be temporarily clamped to each other or to other objects. DAVID WRIGHT reports

Annoyance doesn’t have to be unproductive. Dr Brian Wybrow used to get annoyed when he put his hand in a peg bag and pulled out one by the wrong end. It encouraged him to think there might be a better way to design a peg. The result is an innovative double-ended clamp, manufactured entirely in acetal.

When one end of the clamp is squeezed, the other opens. The jaws can clamp and release objects independently of each other. An easy way to fasten small objects together, the clamp can have many applications. Wybrow says his double-ended clamp (DEC) will be useful in tidying up cables and tubing in the automotive, aerospace and electronic industries, as well as in medical environments. But the uses could be as domestic as attaching a pair of trousers to a hanger or hanging a decoration from a Christmas tree.

At first sight, the clamp looks deceptively simple. The secret lies in the integral spring design. Two identical parts snap fit together to form two natural fulcrums. Avoiding the metal torsion spring used in pegs altogether, Wybrow chose engineering thermoplastics from the Ticona to manufacture the two components. Each have spring arms either side of the snap-fit centre. The two parts can’t slide because of staggered keyways. When the two fulcrums snap together at the centre, the restoring forces in the spring elements create clamping pressure at the jaws

Jaws with real bite

The design can be modified to suit a particular task. The jaws, for example, can be modified to have flat contours and contain more than one pair of curved ‘cable grippers’. Arrays of the clamp could be stuck together and it can be made in almost any size. Wybrow says his clamp can be designed to create any jaw clamping pressure, by snap-fitting two identical fulcrums together. The spring can also be manufactured into an all-plastic single-ended clamp.

Instead of two fulcrums, the DEC could be moulded in one piece, although this has its limitations. The clamping of one pair of jaws would still cause clamping pressure at the other pair of jaws, but when clipping thin objects, such as paper, the first clamping of jaws does not provide sufficient pressure at the other pair to clip another piece of paper.

The materials selected for manufacture depends on the application. Wybrow worked in close cooperation with his material supplier Ticona and the toolmakers and injection moulders Adreco. If flame retardancy isn’t crucial, the C13031 grade of Hastoform acetal copolymer (POM) can be used. On the other hand, for applications which require UL94V-0 flammability ratings, the 2016 grade of Celanex thermoplastic polyester (PBT) is suitable. An area where this might come in useful is in automotive manufacture, to attach cables in the car, such as in wire harnesses and cables under the bonnet.

Wybrow presented a CAD model of his design to Ticona’s Milton Keynes technical centre, which performed a series of finite element analyses with MARC software. An important factor was to get the thickness of the plastic right in particular areas, to ensure a strong clipping force but no creep. The results of the analyses allowed the design to be optimised to provide the lowest and most even levels of stress and strain possible. Because it is a complex shape, Ticona also performed flow analyses which established the ideal gate position and ensured the component would fill correctly.

To evaluate the design further, Adreco produced a prototype tool. Adreco machined a cavity and core into inserts which could then be fitted to the Ticona standard bolster system. This system allows prototype tooling to be produced much more economically and quickly than conventional methods. Inserts can be modified to meet any changes in part design dictated by the test results.

The invention was shown publicly for the first time at the Tomorrow’s World Live Event in London. It received a highly commended award. Several patents which describe a number of product variants are pending, and Wybrow would like to form a joint venture with a firm that can manufacture and market the clamps.

• Wybrow

May 2000

New equipment being introduced by Loctite for metering and dispensing fluids and pastes includes systems which cost at least 25% less than systems previously available. Alan Quinn braved the A1 to take a look.

The need to improve quality, increase productivity and reduce waste has combined with Health and Safety regulations to drive manufacturers towards the use of dispensing and metering equipment. Whether manually actuated or automatically controlled, dispensing equipment ensures that a specified amount of fluid or paste is placed in a defined position with a consistent and repeatable accuracy. Operators do not touch the applied products, workplaces remain clean and the potential for misuse of the products is minimised.

And the complete control of the application ensures that, compared with manual methods, product savings can be as high as 50%. And you can add to this the ability of dispensing equipment to maintain the application of assembly fluids at speeds which are beyond human capabilities.

Loctite’s new integrated semi-automatic system, which will apply consistently accurate doses of ink, oil, paint, flowable greases and solder pastes, costs (UK pounds)882. A comparable system would previously have cost more than (UK pounds)1500.

You get a free-standing unit which simplifies air and fluid supply lines by combining reservoir and controller. An integral pressurised reservoir system uses an infinitely variable electronic control to dispense quantities as small as 0.003ml. Features include a lockable 0 to 4 bar pressure regulator with analogue gauge, 0.04 to 99.9s digital timer, automatically vented tank and an applicator holder. A variety of precision dispensing valves is availalable, and there is the option of a digital low-level alarm.

Loctite’s range also includes manual systems. The simplest product uses a hand pump which is screwed to standard bottles. It provides roving service engineers, fitters and maintenance staff with a portable dispenser applying 0.01 to 0.1ml quantities of anaerobic adhesives and sealants having viscosities of up to 1000mPas.

Other manually-operated dispensers include single and double cartridge guns fitted with pressure regulators to enable the user to control flow rate, and quick pressure relief mechanism. Also available are pneumatic versions of these cartridge guns, for 315ml cartridges and 310ml and 570ml sachets, which will auto-mix two-pack products.

Precision beading

Another air-operated manual unit is the basic ‘integrated’ dispensing system. This was developed for precision beading, potting and free-running deposits. It is available in low and high pressure versions, enabling users to apply thin liquids or high viscosity pastes with extreme control and accuracy. It has adjustable gauge and lockable pressure regulator, and is supplied with either the patented Varidrop or hand-held applicator valve.

The Loctite syringe dispense system is also simple in concept. Two versions – analogue and digital – have been developed for use with refillable 10ml syringes. Both use pressure/time control to dispense dots, drops or small continuous beads, have anti-drip suck-back, can apply products varying from water-thin to paste, and are claimed to increase productivity by 60% whilst reducing waste by 30%. Both semi- and fully-automatic systems are available with separate reservoirs and controllers, for use where it is desirable that the controller is situated some distance from the liquid supply or application.

Features of the semi-automatic modular system include a regulator to prevent air pressure fluctuation, combined power and air on/off switching, digital pressure read-out with electronic monitoring, fluid level sensor and a variety of dispense valves. Additional features of the fully-automatic modular system are an independent, programmable single or two-channel controller, and multi-function control of valves and peripheral equipment. A PLC interface lets you integrate the system into automated production lines.

The new equipment also features standard UV curing systems which range from the simple to the sophisticated. They provide the correct UV light source to match the characteristics of the adhesive or coating to be irradiated and the cure requirements of light intensity and length of exposure.

• Loctite UK

March 2000

Phil Mould Managing Director of TRAQ Fasteners introduces the Bi_Fix range of quarter-turn fasteners ideal for use in most industries where access reliability and aesthetics are equally important.

The Bi-Fix quarter-turn fastener is used for securing panels and components where accessibility is important. It can be used wherever two elements have to be fastened and detached in a quick and safe manner. It is an attractive solution for the maintenance of machines and installations. The special characteristic is the quick and simple detachability. A 90deg turn of the stud unlocks the connections while finger pressure onto the head of the stud re-clicks the fastener into the locked position. In the locked position the two sides of the clip seize the notches of the stud. This connection cannot be opened by vibration or shocks unless they reach about 100g.

The simplest quarter-turn fastener consists of three parts:

• the stud which is located in the panel (loose part)
• the washer which fixes the stud in a way it cannot be lost
• the spring clip which is firmly installed to the shell

The range of Bi-Fix quarter turn-quick release fasteners includes a large range of self-aligning slam latches a range of enclosure hardware a comprehensive range of container hardware and a wide range of spring latches hasps and hinges not previously available in Europe. The fasteners can be manually or tool operated. Available in three sizes and types other styles and finishes are also available.

TRAQ Fasteners has taken the standard Bi-Fix range and introduced features to the system to offer flexibility on methods of operation retention and fastening. A good example of this is the range of clips or receptacles available with the range. Whilst most needs are covered by the original rivet-on versions variants now available include clip-in versions slide-on or slide-in clips weld-on direct or with secondary weld plate tolerance clips (even a clip-in tolerance clip) and the unique flat clip for use where space is at a premium. Also available is a clip-in clip for specific use with 19in racking systems which has become a standard throughout this industry.

Apart from the three standard head styles of the Bi-Fix studs there are no real restrictions on the type of head available from secure options where keys are needed to hinged wire forms. It is of course possible to manufacture the studs with any head or shank shape and for large volumes other manufacturing processes are available for instance a full range of plastic studs is already in the range.

The extensive range of clips and studs is complemented by an equally large choice of retainers including some that allow for the take-up of tolerances be they large or small. Where a more easily operated fastener is required a full range of spherical or pull-push studs is available which work on the principle of push to close and pull to open.

The range of self aligning slam latches has been the main area of product development to take place in the industry for years. All 11 Series Bi-Fix slam latches are available in most finishes and some with variable stud lengths facilitating use with any panel thickness up to about 65mm as standard. All but the plastic version are available with brass steel or stainless steel studs with housings and heads manufactured from zinc alloy.

All 16 Series Bi-Fix Slam latches are available in most finishes with all versions having stud lengths and stud materials to suit requirements. Alternative head types can be easily and inexpensively manufactured to incorporate company logos or varying shapes. Bi-Fix slam latches are aesthetically pleasing manufactured to high quality standards providing flexibility strength vibration resistance and an easily operated fastening system.

• TRAQ Fasteners
• Phil Mould
• 0121 520 7400

July 1998

Looking for a cost effective alternative to weld nuts? Alan Quinn reports on the Kaptinut

There are many alternative captive fasteners available for the sheet metal industry, each with its own benefits and disadvantages. The Kaptinut is a cost-effective alternative to weld nuts in high volume automotive, appliance and other sheet metal applications.

Weld nuts suffer from a number of disadvantages, including:

• Weld splatter
• Distortion of the panel owing to heat, with ever thinner panels exacerbating the problem
• Unsuitable for use on plated panels
• Creation of noxious fumes
• Additional cost and inconvenience of a secondary operation
• There is no easy method of telling if the weld has taken successfully.

The Kaptinut is a high strength, captive threaded fastener system – a range of nuts permanently attached to a panel or component by a mechanical process which requires no heat, electricity, chemicals or adhesives. They are ideally suited to multiple and automated insertion into thin gauge steel, aluminium and pre-finished materials. Kaptinut can offer substantial improvements to product quality whilst reducing in-place costs.

Kaptinut fasteners are available in ISO metric coarse pitch series thread sizes from M4 to M10 and the finished nuts conform to the mechanical properties required for a BS3692 Grade 8 nut.

The finished installation allows for visual inspection, ensuring product quality and confidence at all stages of manufacturing. Kaptinuts can be assembled from either side, as “pull-through” strength is comparable to “push out” strength. This improves flexibility of manufacture.

Installation is a simple, single stroke pressing operation. The nut can be manually fed on a basic fly press or there can be fully

automated multiple insertions within a multi-stage progression tool and press. Overall volume and economies will dictate the best options, but installing the fasteners at the same time as manufacturing the components offers considerable cost-saving opportunities by eliminating the need for a second operation. As the nut installation forms the component, it introduces rigidity into the component and the fastening, resulting in higher bending moment. A near-flush finish is achieved on one side of the component and the fasteners can be plated before or after installation.

Other benefits include:

• Square nut/4 spline design – a square nut in a round hole – enabling optimum material flow between splines and therefore high torque resistance.
• Rolled internal threads which provide higher strength than traditional cut threads
• Modular die design, enabling material thicknesses up to 3.5mm to be accommodated using only one die body
• Zero defect quality designed into the manufacturing process using state of the art six station nut forming and thread forming machines, capable of producing up to 500 nuts per minute
• Low cost automated feed systems.

There is only one nut for each thread size. Varying the tool die accommodates variances in component thickness, thus minimising stocking requirements.

• Kaptifast