Procedure for Measuring Door Closing Force and Striker Bolt Load

INTRODUCTION

This document describes procedures and methods for measuring door closing force (DCF) and striker bolt load (SBL). One method will be discussed for measuring door-closing force (DCF) and two methods for measuring striker bolt load (SBL).
Equipment necessary for performing these measurements are:
  • Data Acquisition System
  • Laptop PC
  • Rotary potentiometer
  • Load transducer (load cell)
  • Power Supply, 13VDC (to supply an external voltage to the potentiometer)

DEFINITIONS

Door closing force (DCF)
The load required to close the door to the fully latched position (latch in primary location).
Striker bolt load (SBL)
The load applied to the striker bolt, from the rotors of the latch, when the door is closed fully.

MEASURING DOOR CLOSING FORCE (DCF)

Use a V.I. (virtual instrument) that can measure load (lbf) vs displacement (degrees). The potentiometer will be used to measure displacement and load cell used for measuring load. Position potentiometer on cab, so displacement of the door can be measured.
Start the V.I. With the door open, apply the load to the door to close it, in a direction through the axial centerline of striker bolt (perpendicular to the longitudinal axis of striker bolt). Use means to ensure placement of the loading component (rubber pad) is placed at the same location for each measurement. Continue to apply load to door (slowly, constant, steady) until the latch reaches the primary position (fully closed). When the primary position is detected, stop applying force to door. The peak measurement acquired at Point A (graph 1) is the door closing force (DCF).
Method 1 - Measuring Striker Bolt Load (SBL), with door open
Immediately after measuring the DCF (as described above), relieve the load to the door (slowly, constant and steadily) until the load is transferred from the load cell onto the striker bolt. At this point, stop the V.I. This measurement should produce a signal, displayed on the graph, similar to GRAPH 1.
GRAPH 1
3 data points are identified on this graph. Point A refers to the door closing force (DCF). Point B refers to the striker bolt load (SBL). Point B refers to where the door has come to rest (stopped moving). Notice Point C is extrapolated vertically from Point B. The theory is that when the door has stopped moving, Point C should be the load that is exerted onto the striker bolt (SBL).
Method 2 - Measuring Striker Bolt (SBL), w/door closed.
In this method, use the same equipment as in Method 1. Close the door fully. Using load cell and assembly to apply force to door, place the rubber bumper (w/load cell in-line) through the longitudinal axis and midway of shoulder height. (same as Method 1).
Apply force to door until door moves 130% greater than DCF. You should move the door enough so the load created by the seal and door is transferred from the striker bolt to the load cell. When you have reached this point, relieve the load on the door slowly until all load is transferred back to the striker bolt.
The signal displayed on the graph should be similar to Graph 2. The portion of the curve that is of most interest is illustrated in the Graph 2. As the graph shows, when applying a load to the door initially, the displacement should stay the same while the load increases. At Point A, the displacement starts to change (door moving). This portion of the curve is of most interest. This is when the load is transferring from the striker bolt onto the load cell. Point A represents the SBL, low end of range.
GRAPH 2

SUMMARY

By measuring these loads in a laboratory environment, we had the benefit of being able to measure the actual SBL, so we could compare this value to the methods mentioned in this document. This actual SBL measurement was accomplished by placing a load cell in-line with the striker bolt. The cab had to be modified to measure the actual SBL.
By measuring these loads as described in Methods 1&2, we should be able to identify a SBL range. Method 1 will typically represent the high end of the SBL range, due to the fact that with this method we are compressing a fully relaxed door seal. Method 2 will typically represent the low end of the SBL range, due to the fact that the door seal is already compressed (some air in pores of gasket are removed). When the door is opened (latch actuated), this load is what is going to be closer to what is actually applied to the latch, during actuation.
If further information is desired, please contact the TriMark Test Engineering Department.
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