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Screws for Plastics with Flat Countersunk Head
Screws for Plastics with Flat Countersunk Head
Screws for Plastics with Flat Countersunk Head
Screws for Plastics with Flat Countersunk Head
Screws for Plastics with Flat Countersunk Head

Flat Countersunk Head Screws for Plastics

Specially designed for high strength assemblies in Thermo Plastics.  Coarse thread for high pullout and stripping torque.  30 degree thread crest angle for low driving torque and high repeat assembly.  Optimum helix angle to give high resistance to vibration

Available in stainless steel, zinc plated hardened steel, and black plated hardened steel.  With TX, Phil or Pozi recess. See size chart for details

Diameters - 2.5mm, 3.0mm, 3.5mm, 4.0mm & 5.0mm

100 pcs per bag

Click on the images to enlarge

Design Considerations

Recommendations for boss geometry

For obvious reasons of enconomy, emphasis is placed on making bosses as small as possible.  This also helps to reduce flaws during moulding.  Bosses should, in principle, conform to the sketch shown in the image.  Experiments on test mouldings have given guide values for Screw Hole Diameter (dl) Boss Diameter (D) and Penetration Depth (te).  See image for details

If modification of the boss is required the following steps should be taken in order to reduce expansion.

1) Reduce external boss diameter
2) Increase screw hole diameter
3) Increase penetration depth

Calculation of Tightening Torques

Tightening torques should be kept to the minimum necessary in order to avoid excess strain on the plastic material, as this always results in relaxation. Whilst a mean tightening torque might be selected (see formula in image), relaxation would be further avoided by selecting the minimum necessary to achieve the desired clamping load, allowing for repeat accuracy of the screw driver

Repeat accuracy values obtained over many years experience

Electric driver with claw coupling   ± 30%
Electric precision driver ±  3 to 5%
Pneumatic driver with cut-out ±  15%
Pneumatic precision driver ±  3 to 5%

Effect of Drive Speeds on Performance

Whilst driving torques reduce with increased speed, the improvement in stripping torques due to increasing strain rate in the thermoplastic is only initial. Over 500 rpm, a steady decline in values can be seen (see image graph) For this reason screw drivers should not exceed a set speed of 500/600 rpm

Recommendations for Assembly

Driving Torque (ME) - This is the torque required to deform thermoplastic and overcome frictional resistance.

Stripping Torque (MU) - This is the torque required to shear the formed female thread in the thermoplastic

For a reliable assembly, the maximum possible difference between driving and stripping torques is desireable, since this governs the clamping force that can be induced in the assemby.  (See image)

Driving Torque always decreases with increases in hole diameter.  Stripping Torque increases as hole diameter increases (a reflection of the reduction in material stress) to a certain value beyond which the stripping torque decreases.  The point at which there is greater difference between mean values (after application of 99.8% confidence interval) is the optimum screw hole diameter.  (See image graph)

The data and figures specified are to be used as a guide only.  We recommend you conduct your own assembly tests to determin the optimum values

  • Diameter (mm):2.5 mm, 3 mm, 3.5 mm, 4 mm, 5 mm
  • Colour:Black, Stainless, Zinc
  • Drive Type:Phillips, Pozi, TX
  • Head Type:Flange
£3.70ex. VAT £4.44inc. VAT bag of 100
Option 1 - 9 bags10 - 19 bags20+ bags
2.5 x 8 Pozi Zinc  £6.22£5.33£4.44
2.5 x 10 Pozi Zinc  £6.38£5.47£4.56
3.0 x 6 Pozi Black  £6.30£5.40£4.50
3.0 x 10 Pozi Zinc  £6.72£5.76£4.80
3.0 x 10 TX Zinc  £6.72£5.76£4.80
3.0 x 12 Pozi Zinc  £7.14£6.12£5.10
3.5 x 10 Pozi Zinc  £7.39£6.34£5.28
3.5 x 16 Pozi Zinc  £8.90£7.63£6.36
3.5 x 16 Stainless Pozi  £23.52£20.16£16.80
3.5 x 16 Phil Zinc  £8.90£7.63£6.36
4.0 x 10 Pozi Zinc  £8.57£7.34£6.12
5.0 x 20 TX Zinc  £18.48£15.84£13.20
5.0 x 20 Stainless TX  £31.92£27.36£22.80
5.0 x 25 Stainless TX  £35.28£30.24£25.20
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