how to set value in text_field and store these value into database table in rails

These things i have all ready done, but at that time the value of text_field is not insert into database table, reaming value insert successfully but one value is not inserted.

I can understand where am i wrong and what is missing...

_employee_details.html.erb

<%= form_for(:employee_details, :url => {:controller => 'hr', :action => 'create'}) do |f| %>
       <%= f.text_field :employee_id, { :value=> "123548", :disabled=>true , :required => true, placeholder: 'E12345678', class: 'form-control' } %>
<% end %>

hr_controller.rb

class HrController < ApplicationController

    def new
        @employees = EmployeeDetail.new
    end

    def create
        @employees = EmployeeDetail.new(employee_params)
        if @employees.save
            redirect_to :action => 'internal_employee_page'
        else
            redirect_to :action => 'internal_employee_page'
        end
    end

    private

        def employee_params
             params.require(:employee_details).permit(:offer_letter_id, :employee_id, :bank_ac, :bank_ifsc, :spouse_name, :gender, :work_end_date)
        end     
end

All value is successfully insert into employee_details table accept employee_id

employee_details.rb this is my modal

class EmployeeDetail < ActiveRecord::Base 
    belongs_to :user
    validates :offer_letter_id, presence: true 
end

I have already try this but this is not working